1. Field of the Invention
The present invention relates to an image stabilization apparatus and control methods for such an image stabilization apparatus, an optical apparatus, and an imaging apparatus that compensate image blur (image degradation) caused by shakes such as handshakes.
2. Description of the Related Art
At present, cameras provided with image stabilization apparatuses that prevent image blur caused by handshakes and are configured with, for example, a shake compensation unit, a driving unit, and a shake detection unit are in commercial production, and as a result, user-caused shooting mistakes are decreasing.
As an example of an image stabilization apparatus, an apparatus that detects rotational shakes by using an angular velocity sensor and moves a part of the lens or an image sensor so as to reduce image blur on the image sensor surface is incorporated in various optical apparatuses as an effective image blur correcting function. However, in close-range shooting or high-magnification ratio shooting, image degradation caused by so-called “translational shakes (parallel shakes)”, which are applied in a parallel or perpendicular direction to the optical axis of the camera and cannot be detected by an angular velocity sensor alone, cannot be ignored.
Here, a description will be given of a conventional camera incorporating an image stabilization apparatus that performs image blur correction by detecting rotational shakes and translational shakes, with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating shake directions of a camera 101, and FIG. 2 is a diagram showing the top view of the camera 101 and an image stabilization processing unit provided in a camera CPU 106 incorporated in the camera 101. The image stabilization system incorporated in the camera 101 performs correction on the shakes (hereinafter referred to as rotational shakes) indicated by arrows 103p and 103y and on the shakes (hereinafter referred to as translational shakes) indicated by arrows 104p and 104y, with respect to an optical axis 102.
The camera 101 also includes a release button 105, the camera CPU 106, an image sensor 107, an angular velocity sensor 108 that detects the rotational shakes 103p and 103y, an acceleration sensor 109 that detects the translational shakes 104p and 104y, a driving unit 110 and an image stabilization mechanism 111. The driving unit 110 causes the image stabilization mechanism 111 to drive a correction lens so as to perform image stabilization taking both rotational shakes and translational shakes into account.
An angular velocity signal from the angular velocity sensor 108 and an acceleration signal from the acceleration sensor 109 are input into the camera CPU 106. In the camera CPU 106, a rotational shake correction amount calculation unit 106a calculates a rotational shake correction amount, and a translational shake correction amount calculation unit 106b calculates a translational shake correction amount. The calculated rotational shake correction amount and translational shake correction amount are summed together (combined) by an addition unit 112. Image stabilization is then performed based on the correction amount obtained in the above-described manner.
Japanese Patent Laid-Open No. 7-225405 discloses a technique where an acceleration sensor that detects acceleration is provided, translational shakes (parallel shakes) are found from a second-order integral of the acceleration obtained by the acceleration sensor, and a shake compensation unit is driven based on the translational shake and the output of a separate angular velocity sensor.
However, the output of the acceleration sensor used to detect translational shakes is susceptible to environmental changes such as noise from disturbances, changes in temperature, and so on, and because such unstable factors are exacerbated by taking the second-order integral, there is a problem in that highly-precise translational shake compensation is difficult to achieve.
Meanwhile, Japanese Patent Laid-Open No. 2010-25962 discloses handling translational shakes as rotational shakes when the center of rotation is located in a position that is distant from the camera. With this method, an angular velocity sensor and an acceleration sensor are provided, and shake compensation is carried out by finding a compensation value and an angle using the radius of rotation of the rotational shake based on the output from the sensors; through this, a center of rotation that is limited to a frequency band unsusceptible to disturbances is found. Doing so makes it possible to reduce unstable factors in the acceleration sensor as described above.
However, the method for performing translational shake correction has the following problems. The first problem is that, in order to perform translational shake correction, it is necessary to provide a translational shake detection sensor, but if, for example, an acceleration sensor is used as the translational shake detection sensor, it may cause an increase in the size of the camera and the cost. Another problem is that it is desirable to attach the acceleration sensor to the lens principal point position, but it is difficult to provide an acceleration sensor near the lens principal point position.
Japanese Patent Laid-Open No. 2010-25962 discloses a method in which, in order to detect translational shakes, the shakes are detected based on output from an image sensor, instead of an acceleration sensor. In the case of detecting shakes based on output from an imaging unit, a method is used in which a correction coefficient is calculated based on a relationship between image blur and rotational shakes immediately before a photographing operation and correction is performed on rotational shakes during the photographing operation. In this case, however, a problem arises in that the translational shake correction can be performed only during a photographing operation. In moving image shooting, control is possible by electric image stabilization in which a correction coefficient is obtained based on the relationship between image blur and rotational shakes, the obtained correction coefficient is multiplied by rotational shakes to calculate a translational shake amount, and the position of an area clipped from an image formed on the image sensor is changed according to the calculated translational shake amount. This, however, also causes problems in which an angle of view is narrowed due to clipping of a part of an image.
Japanese Patent Laid-Open No. 2010-25962 also discloses the use of, as a shake detection unit, a unit that detects acceleration of translational shakes based on current generated in a driving coil, instead of an acceleration sensor. However, with the unit that detects acceleration of translational shakes based on current generated in a driving coil, it is not possible to perform image stabilization control until immediately before a photographing operation. In the case where the influence of translational shakes is large such as in the case of macrophotography, it may be difficult to set a fine configuration or achieve accurate focus. There is also another problem in that during moving image shooting, the translational shake correction cannot be performed. Also, the acceleration estimation using a coil current value does not give consideration to the characteristics of the image stabilization mechanism, and therefore it is difficult to perform accurate acceleration estimation, and the use of estimated acceleration in image stabilization presents a problem with the accuracy of estimation.